1. Field Of The Invention
The present invention relates to the monitoring of the quantity of a web, sheet or strand material wrapped upon itself about a reel.
More specifically, the present invention relates to an apparatus for measuring the diminishing diameter of a web or sheet material supply reel for the purpose of initiating a splice transfer at an economically optimum moment.
2. Description Of The Prior Art
Various paper web converting operations such as printing, embossing and corrugating utilize a turret type unwind strand having two or more spider arms to axially mount respective reels of paper web. As the web from one reel is exhausted, the leading edge of a fresh reel is secured to the tail of the exhausted reel web for the uninterrupted continuation of the web supply. As the fresh reel diminishes, the turret spider is rotated to the first position and another fresh reel is mounted in readiness.
At a constant web withdrawal rate in the order of 600 fpm (185 meters per minute) for example, acceleration of the supply spool makes it very difficult to consistently anticipate the web ending for the purpose of splicing thereto the leading edge of a fresh roll. Conversely, the normal practice of completing the splice cautiously in advance of the foregoing web tail is, by virtue of cumulative absolutes, the source of considerable web wastage.
In the past, numerous techniques have been devised to eliminate the inconsistency of manual judgment from the web splicing unit. Such techniques have included rider rolis designed to throw a limit switch when the rider reaches a predetermined arcuate position relative to the critically small diameter of the diminishing supply reel. Although simple, the mechanism for this technique is exposed and vulnerable to considerable abuse. Moreover, although more consistently accurate (when operative) than human judgment, this device lacks for desired accuracy.
Another prior art technique for anticipating a web reel end includes apparatus for measuring web linear velocity and the angular velocity of the diminishing reel. An analog comparison is made of these two measurements and when the appropriate combination is reached for a predetermined reel diameter, an alarm or other appropriate signal is issued. While this technique eliminates the presence of appurtenant structure subject to operational damage, due to tolerance limits of analog indicators and the accuracy thereof, further room remains for improvement.